Stenting is now a commonly accepted procedure to maintain the patency of vessels following angioplasty, and has gained widespread acceptance for the treatment of blockages of the cardiac arteries. Numerous stent designs are known in the prior art, including balloon expandable slotted tube stents, such as described in U.S. Pat. No. 4,733,665 to Palmaz, radially self-expanding zig-zag structures, such as described in U.S. Pat. No. 4,580,568 to Gianturco, and self-expanding wire-mesh structures, such as described in U.S. Pat. No. 4,655,771 to Wallsten. Each of these previously-known stents provides a mix of ease-of-delivery and deployment, radial strength, crush resistance and other characteristics.
Despite the wide variety of stent structures available, there are certain vessels within the body that pose unique challenges for previously-known stent and stent delivery system designs. One such vessel is the renal artery. The relatively short length of the renal artery and the manner in which it branches from the abdominal aorta, often make access and deployment of previously-known stents difficult. Because renal artery lesions often occur at the renal ostium, the treatment of such lesions pose unique problems relating to embolization of plaque liberated during angioplasty. In addition, deployment of a stent across an ostial lesion can result in a portion of the stent extending into the abdominal aorta that may serve as a site of thrombus formation and also make re-access to the vessel virtually impossible.
A number of catheter-based systems are known that attempt to address the problem of embolization resulting from the disruption of plaque during balloon dilatation. Such systems may be independent of the stent delivery system or form a part thereof, and generally may be classified as either “proximal” or “distal” emboli protection systems. Proximal emboli protection systems, such as described in U.S. Pat. No. 5,833,650 to Imran et al. and U.S. Pat. No. 6,295,989 to Connors, generally place an occlusion element upstream of a lesion to prevent antegrade blood flow through the vessel during angioplasty; suction is applied to aspirate emboli-laden blood proximally through the catheter prior to restoring antegrade flow. Distal emboli protection systems, such as described in U.S. Pat. No. 4,723,549 to Wholey and U.S. Pat. No. 5,814,064 to Daniel et al. employ a blood permeable filter element that is placed downstream of the stenosis to filter emboli released during angioplasty.
Currently, none of the foregoing previously-known emboli protection systems perform reliably when used in renal artery angioplasty or stenting. For example, due to the relatively short length of the renal artery, there may be insufficient distance to deploy the filter element of a distal emboli protection system. In such cases, the perimeter of the filter element may not positively seal against the vessel wall, thereby permitting emboli to bypass the filter element and travel downstream to lodge in, and occlude, smaller vessels.
In addition, the relatively short length of the renal artery makes it difficult to place a filter in the renal artery. The filter frame and/or filter material typically make the filter axially stiff and impede tracking of the filter around the steep angulation at the renal ostium. The renal artery often has an inferior angle of origin from the aorta and then immediately projects posteriorly, thereby further amplifying difficulty in accessing the renal artery from a femoral artery approach.
Further, most filter designs employ a retrieval catheter that is advanced over the filter to contract the filter prior to removal. Such retrieval catheters may not conform to the wire and may get caught on the filter, thereby rendering retrieval impossible. In such cases the filter must be forcibly removed, with the attendant risk that the filter may become entangled in the stent and/or traumatize the artery requiring emergent surgical repair.
A wire having a distal occlusion balloon, such as described in the above patent to Connors, presents similar drawbacks in renal artery applications. For example, the presence of the balloon changes the axial stiffness of the wire and enhances the difficulty in tracking across severe angle encountered at the renal ostium. In addition, inflation of the distal balloon applies tension to the wire that may inflict trauma on the renal artery when a stent delivery catheter is then advanced around the abrupt angle bend at the renal artery ostium. A further drawback common to both the distal occlusion balloon and filter systems is the presence of the balloon or filter wire, which may limit the clinician's options when accessing and treating complex lesions.
Still other problems may arise in attempting to use a distal balloon emboli protection system in a renal artery. Again, because of the relatively short length of the renal artery, it is possible to dislodge the distal occlusion element during manipulation of the angioplasty balloon catheter and/or stent delivery system, thus permitting emboli to bypass the occlusion element. While the potential for dislodging the occlusion element, e.g., balloon, may be reduced by use of a compliant balloon, such use raises other potential problems. Specifically, use of a compliant balloon enhances the risk of perforating or “jailing” the balloon during stent deployment. In the former case the balloon may inadvertently deflate, enabling the emboli to bypass the balloon and flow downstream. In the latter situation, the stent traps a portion of the balloon against the vessel wall, making it difficult or impossible to retrieve the occlusion element and necessitating surgical intervention.
Eighty percent of renal artery lesions are ostial and thus proximal balloon protection systems will not work in the majority of cases. The majority of the remaining “non-ostial” renal artery lesions occur within the first centimeter of the renal origin. In such cases, proximal balloon occlusion may be employed in only a very small number of patients. Accordingly, the use of previously-known proximal protection systems during renal stenting is not viable solution.
As noted above, still other problems have limited the acceptance of stenting in the treatment of renal artery disease. These problems arise both from the anatomy of the vessel and the types of lesions that are observed. Not only is the renal artery relatively short, but it also is difficult to access from percutaneous access sites in the groin region, because the arteries tend to branch in a descending manner from the abdominal aorta. As a result, it is often difficult to visualize the arteries under fluoroscopic guidance, and even more difficult to determine accurate placement of a stent delivery system in such vessels.
Because many renal artery lesions occur at the ostia of the vessels as noted above, inaccurate stent placement may result in either incomplete coverage of the lesion (with attendant restenosis) or the stent may project excessively into the abdominal aorta and serve as a site of thrombus formation. In addition, in the latter case the projecting portion of the stent may make further access to that renal artery impossible. Although some attempts for addressing these issues have been made, such as disclosed in U.S. Pat. No. 5,749,890 to Shaknovich, such systems do not permit the clinician to precisely determine the location and orientation of the stent delivery system relative to the ostium prior to stent deployment.
To date, the successful use of stents to treat renal artery obstructions has been limited to a relatively few clinicians with extraordinary skill gained from extensive experience in this area. It therefore would be desirable to provide apparatus and methods that enable a broader cross-section of interventional clinicians to effectively treat renal artery disease.
Accordingly, it would be desirable to provide apparatus and methods that enable removal of emboli liberated during balloon dilatation or other treatment of the renal artery, and that account for the peculiar anatomy of that vessel.
It further would be desirable to provide apparatus and methods that permit an emboli protection system to be used in conjunction with angioplasty and stenting of the renal arteries with reduced risk of complications.
It further would be desirable to provide apparatus and methods that facilitate accurate determination of stent placement within a renal artery prior to deployment of a stent.